Method of manufacturing microlens array and microlens array

ABSTRACT

A method of manufacturing a microlens array comprising forming microlenses by dropping or injecting to a plurality of through holes formed on a substrate a liquefied lens material so as to dispose the lens material at each of the through holes, the lens material being curable and has a predetermined transmittivity and a predetermined viscosity.

This application is a divisional of U.S. patent application Ser. No.10/126,726, filed Apr. 19, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microlens array typically used in thefields of optical communication and optical packaging for coupling lightemitted from a light source to an optical fiber or an optical waveguide,converting light emitted from the optical fiber or the optical waveguideinto parallel rays or so focusing light beams to enter the optical fiberor the optical waveguide in an optical coupling system.

2. Related Art of the Invention

The microlens in general represents a fine lens having a lens diameterof not more than a several millimeters. Various methods relating to themicrolens array including methods for manufacturing the same have beenproposed in the art. The ion exchange diffusion method is widely knownas a method for manufacturing the microlens array. In the ion exchangediffusion method, a dopant ion is selectively diffused on amulticomponent glass substrate.

The conventional ion exchange diffusion method will be described belowwith reference to FIGS. 14A to 14C. As shown in FIG. 14A, an ionexchange control membrane 102 is firstly formed on a surface of amulticomponent glass substrate 101 containing a monovalent ion. The ionexchange control membrane 102 may be a metal membrane or a dielectricmembrane. Next, an array of circular apertures 103 at a predeterminedpitch that is equivalent to that of an LD array or a PD array is formedon the ion exchange control membrane 102 using a photolithographictechnique or a etching technique. The diameter of a lens preparedaccording to this method is determined by each of the apertures 103, andthe apertures function as light-shielding membranes for reducingcrosstalk between adjacent channels.

High temperature molten salt 104 shown in FIG. 14B containing a dopantion that will contribute to ascending in refractive index. The dopantion may include Tl, Ag and Pb, each having a high degree of refractiveindex. Then, the glass substrate 101 that is coated with the ionexchange control membrane 102 having the circular apertures 103 isimmersed in the molten salt 104 so that the dopant ion is selectivelydiffused on the glass substrate 101 through the apertures 103 on the ionexchange control membrane 102 to thereby form ion exchange areas 105each having a hemispheric diffusion front. The ion exchange areas 105serve as distributed refraction type lenses according to a dopant iondistribution. Here, as a result of selecting the dopant ion having theion radius that is larger than that of the ion contained in the glasssubstrate 101, the surface of the substrate 101 is expanded according tothe volumetric difference between the ions to form convex lenses 106shown in FIG. 14C. A diameter of each of the convex lenses 106 istypically in a range of from a several tens of microns to a severalhundreds of microns.

The above-illustrated ion exchange diffusion method is suitable forforming a microlens having a diameter of from a several tens of micronsto a several hundreds of microns; however, problems have been found withthe method in manufacture of a microlens having a relatively large lensdiameter or a lens effective diameter of from a several hundreds ofmicrons to a several millimeters. More specifically, in order to preparethe relatively large microlens employing the ion exchange diffusionmethod, a depth of the diffusion must be a several hundreds of micronsor more that is about the same as the size of the lens to be producedand it is necessary to conduct a heat treatment at a high temperaturefor a remarkably long time. Thus, in the ion exchange diffusion method,it is difficult to prepare lenses of a wide range of sizes havingdiameters from a several tens of microns to a several millimeters and,also, it is impossible to produce a microlens array having a focallength that is about the same as that of the diameter of the lens.Therefore, downsized and high-performance optical coupling elements havenot been realized by the use of the ion exchange diffusion method.

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide a method of manufacturing a microlens array that realizesdownsized and high-performance optical coupling elements to be used inthe fields of optical communication and optical packaging.

One aspect of the present invention is a method of manufacturing amicrolens array comprising forming microlenses by dropping or injectingto a plurality of through holes formed on a substrate a liquefied lensmaterial so as to dispose the lens material at each of the throughholes, the lens material being curable and has a predeterminedtransmittivity and a predetermined viscosity.

Another aspect of the present invention is the method of manufacturing amicrolens array, wherein a curvature of each of the microlens is variedby adjusting whole or part of (1) configurations or sizes of the throughholes of the substrate, (2) wettability between the substrate and thelens material, (3) a viscosity of the lens material and (4) a quantityof lens material in a droplet or in an injection shot.

Still another aspect of the present invention is the method ofmanufacturing a microlens array, wherein the lens material is dropped orinjected substantially simultaneously by using nozzles that can drop orinject the lens material substantially simultaneously to the throughholes.

Yet still another aspect of the present invention is the method ofmanufacturing a microlens array, wherein the lens material is aultraviolet ray curable resin material, a thermosetting resin material,a thermoplastic material or a glass material.

Still yet another aspect of the present invention is the method ofmanufacturing a microlens array, wherein each of the through holes has atruncated conical shape or a step portion.

A further aspect of the present invention is the method of manufacturinga microlens array, wherein the microlenses are convex lenses.

A still further aspect of the present invention is the method ofmanufacturing a microlens array, wherein the microlenses are concavelenses.

A yet further aspect of the present invention is the method ofmanufacturing a microlens array, wherein all refractive indexes and/or atransmittivities of the lens materials to be dropped or injected to theplurality of through holes are not same.

A still yet further aspect of the present invention is the method ofmanufacturing a microlens array, wherein a whole or a part of theplurality of through holes vary in size, and the lens material isdropped or injected in accordance with the sizes of the through holes.

An additional aspect of the present invention is the method ofmanufacturing a microlens array, wherein the plurality of through holesare arranged on the substrate to give a closest packed structure, eachof the through holes having the shape of a hexagon of a predeterminedsize.

A still additional aspect of the present invention is the method ofmanufacturing a microlens array, wherein the substrate is formed fromsilicone, a plastic material, a glass material, ceramic material, fibermaterial or a composite material.

A yet additional aspect of the present invention is a microlensmultilayer formed by laminating a plurality of microlens arrays producedby the method of manufacturing a microlens array, wherein the pluralityof microlens arrays are so laminated that optical axes of themicrolenses of each microlens array coincide with the optical axes ofthe corresponding microlenses of another microlens array.

A still yet additional aspect of the present invention is a microlensarray comprising a substrate in which a plurality of through holes areformed and a plurality of microlenses respectively disposed at thethrough holes in the substrate, wherein

-   -   the microlenses are fixed to the through holes of the substrate        by way of adhesion or deposition of a microlens material to a        substrate material.

A supplementary aspect of the present invention is the microlens array,wherein the microlenses are formed of a ultraviolet ray curable resinmaterial, a thermosetting resin material, a thermoplastic material or aglass material.

A still supplementary aspect of the present invention is the method ofmanufacturing a microlens array, wherein each of the through holes has atruncated conical shape or a step portion.

A yet supplementary aspect of the present invention is the method ofmanufacturing a microlens array, wherein the microlenses are convexlenses.

A still yet supplementary aspect of the present invention is the methodof manufacturing a microlens array, wherein the microlenses are concavelenses.

Another aspect of the present invention is the method of manufacturing amicrolens array, wherein all refractive indexes and/or atransmittivities of the lens material to be dropped or injected to theplurality of through holes are not same.

Still another aspect of the present invention is the method ofmanufacturing a microlens array, wherein a whole or a part of theplurality of through holes vary in size and a whole or a part of themicrolenses vary in size in accordance with the sizes of the throughholes.

Yet still another aspect of the present invention is the method ofmanufacturing a microlens array, wherein the plurality of through holesare arranged in the substrate to give a closest packed structure, eachof the through holes having the shape of a hexagon of a predeterminedsize.

Still yet another aspect of the present invention is the method ofmanufacturing a microlens array, wherein the substrate is formed of anyone of silicone, a thermoplastic material, a glass material, a ceramicmaterial, a fiber material and a composite material.

A further aspect of the present invention is the method of manufacturinga microlens array, wherein each of the microlenses has a multilayerstructure that consists of a plurality of layers varying in material andrefractive index.

A still further aspect of the present invention is the method ofmanufacturing a microlens array, wherein each of the plurality ofthrough holes in the substrate has a rectangular shape of apredetermined size and each of the microlenses that is formed bydropping has an anamorphotic or cylindrical configuration.

A yet further aspect of the present invention is the method ofmanufacturing a microlens array, comprising subjecting a surface of thesubstrate to an inactivating treatment so that a portion of the surfaceexcluding the through holes has repelling properties to the lensmaterial and the through holes have adhesive properties to the lensmaterial.

A still yet further aspect of the present invention is the method ofmanufacturing a microlens array, wherein the surface of the substrate iscaused to be uneven by the inactivating treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a microlens array according to thefirst embodiment of the present invention.

FIG. 2 is a cross-sectional view of the microlens array according to thefirst embodiment of the present invention.

FIGS. 3A to 3E are illustrations for explaining a method of manufactureof a microlens array according to the second embodiment of the presentinvention.

FIGS. 4A to 4C are illustrations for explaining a method of manufactureof a microlens array according to the third embodiment of the presentinvention.

FIGS. 5A to 5D illustrations for explaining a method of manufacture of amicrolens array according to the fourth embodiment of the presentinvention.

FIGS. 6A to 6D are cross-sectional views for explaining how a curvatureof a lens can be changed by changing a configuration of a through holeaccording to an embodiment of the present invention.

FIGS. 7A to 7C are illustrations for explaining a method of manufactureof a microlens array according to the fifth embodiment of the presentinvention.

FIG. 8 is an illustration for explaining a method of manufacture of amicrolens array according to the sixth embodiment of the presentinvention.

FIGS. 9A and 9B are illustrations for explaining a method of manufactureof a microlens array according to the seventh embodiment of the presentinvention.

FIGS. 10A to 10D are patterns of a microlens array according to theeighth embodiment of the present invention.

FIGS. 11A to 11C are illustrations for explaining a conventional methodof manufacture of a microlens array.

FIGS. 12A and 12B are illustrations for explaining a method ofmanufacture of a microlens array according to the tenth embodiment ofthe present invention.

FIGS. 13A and 13B are illustrations for explaining a method ofmanufacture of a microlens array according to the eleventh embodiment ofthe present invention.

FIGS. 14A to 14C are illustrations for explaining a conventional methodof manufacture of microlens array.

REFERENCE NUMERALS

-   -   11, 31, 51, 61, 71, 81, 83, 85, 87, 91: substrates    -   32, 52, 62, 72: through holes    -   12, 35, 55, 56, 65, 73, 82, 84, 86, 88, 92, 93, 94, 95, 96, 97:        lenses    -   33, 44: nozzles    -   101: multicomponent glass substrate    -   102: ion exchange control membrane    -   103: circular aperture    -   104: molten salt    -   105: ion exchange area    -   106: convex lens

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to FIGS. 1 to 14.

(First Embodiment)

FIG. 1 is a perspective view showing a microlens array according to afirst embodiment of the present invention. As shown in FIG. 1, themicrolens array in the first embodiment comprises a substrate 11 inwhich a plurality of through holes are provided and convex lenses 12arranged on each of the through holes in the substrate 11, wherein adiameter of each of the convex lenses is from about a several tens ofmicrons to about a several millimeters.

The convex lenses 12 have light transmitting properties and they areformed from a curable liquefied resin material or a thermoplasticmaterial or a glass material that can be cured on the substrate 11.

FIG. 2 is a cross-sectional view of the microlens array according to thefirst embodiment of the present invention described above with referenceto FIG. 1, showing a state wherein the convex lenses are respectivelydisposed at the through holes on the substrate 11. As shown in FIG. 2,the lens material extends through the through holes above and below thesubstrate 11.

The microlens array according to the first embodiment is characterizedin that a lens material, which is the resin material or the heated andliquefied plastic material or glass material described above, is droppedor injected to the through holes formed on the substrate 11 and that theconvex lenses are disposed by taking advantages of a surface tension ofthe lens material. Further, positions of the convex lenses can be setarbitrarily depending on positions of the through holes disposed on thesubstrate 11.

Particularly, the positioning of the convex lenses 12 on the substrate11 is facilitated by dropping or injecting the lens material to thethrough holes after forming the through holes on the substrate 11. Thepositions and sizes of the though holes can be defined arbitrarily byemploying a fine processing technique according to the substratematerial and, therefore, it is possible to form the through holes with aremarkably high degree of precision. Further, it is possible to controloptical characteristics of the lenses by properly selecting therefractive index of the lens material. Moreover, it is possible tocontrol a curvature of each of the lenses by adjusting a viscosity ofthe lens material before curing and an amount of drop or injection ofthe lens material to each of the through holes.

Thus, the microlens array according to the first embodiment of thepresent invention is characterized in that the positions and the opticalcharacteristics of the lenses are controlled simultaneously and with aremarkably high degree of precision. Further, it is possible to formlenses of a wide range of effective diameters of from about a severaltens of microns to about a several millimeters by adjusting awettability, a viscosity and an amount of drop of the lens material tothe substrate material.

The microlens array according to the first embodiment of the presentinvention is remarkably advantageous in terms of the optical couplingsince the focal length is about the same as that of the diameter of eachof the lenses and both surfaces of the lens are open to air withoutcontacting the substrate material.

Thus, the material used for forming the substrate 11 of the microlensarray according to the first embodiment of the present invention is notnecessarily an optical material having light transmitting propertiessuch as the plastic material or the glass material. More specifically,it is possible to form the microlens array if the substrate 11 is notformed from the optical material. In the case where the substrate 11 isformed from a material other than the optical material, the substrate 11functions as an optical mask for the lenses to be formed on thesubstrate, thereby preventing stray lights from entering the lenses,which is remarkably effective in practical use.

(Second Embodiment)

FIGS. 3A to 3E are illustrations for a method of manufacturing microlensarray according to a second embodiment of the present invention. Themethod of manufacturing microlens array of the second embodiment in thecase of using a glass material for a substrate 31 and an adhesive resinmaterial having light transmitting properties as a material for lenses35 as shown in FIGS. 3A to 3E will be described in detail below.

As shown in FIG. 3A, through holes 32 are formed on a substrate 31precisely by employing various fine processing techniques. The fineprocessing techniques to be employed may be an ultraprecise cutting, alaser processing, a focusing ion beam processing, a laser etching, amicrodischarging, an electron beam writing.

Then, as shown in FIG. 3B, an adhesive material 34 is dropped from dropnozzles 33. A viscosity of the adhesive material 34 is so selected thatthe adhesive material stays in the through holes 32 without fallingtherefrom as shown in FIG. 3C. The viscosity and dropping amount must beselected properly to prevent the lens material 34 from falling from thethrough holes 32.

The adhesive resin material 34, which is the lens material, is droppedsequentially to the through holes disposed on the substrate as shown inFIG. 3D. The dropped adhesive resin material is then subjected to a heatcuring or a ultraviolet ray curing method depending on characteristicsof the resin to form convex lenses, thereby completing the production ofmicrolens array shown in FIG. 3E. Epoxy-based adhesive resins or thelike having light transmitting properties may be used as a thermosettingresin, while fluoridated epoxy-based resins or the like may be used as aultraviolet ray curable resin.

(Third Embodiment)

A method of manufacturing microlens array according to a thirdembodiment of the present invention that is illustrated in FIGS. 4A to4C will be described below. The process illustrated in FIGS. 4A to 4C isdifferent from that illustrated in FIGS. 3A to 3E by a nozzle unit 44that is formed by integrating a plurality of nozzles in order to shortena time required for the production. By the use of such integrateddropping nozzles 44, a microlens array comprising the plurality ofconvex lenses can be two-dimensionally produced in a remarkably shortperiod and effectively.

(Fourth Embodiment)

A method of manufacturing microlens array according to a fourthembodiment of the present invention that is illustrated in FIGS. 5A to5D will be described below. The process illustrated in FIGS. 5A to 5D isdifferent from that illustrated in FIGS. 4A to 4C in a tapered throughhole 52 that is formed on a substrate 52. That is, the through hole hasa truncated conical shape. The tapering of the through hole 52 makes itpossible to control a curvature of a lens surface of a convex lens 55that is formed on the through hole 52 by dropping a lens material 34from a nozzle 33. In the case where a bottom diameter is fixed, it ispossible to reduce the curvature of each of the lenses, i.e., toincrease a convexity of each of the lenses, by increasing a taperingangle α. In turn, it is possible to form a concave lens shown in FIG. 5Dby reducing the dropping amount.

As shown in FIGS. 5A to 5D, it is possible to change the curvature ofthe lens by changing a configuration of the through hole. Generally, inthe case of dropping a liquid to a surface of a solid, “wet” means thatthe liquid spreads over the solid to cover its surface and “do not wet”means that the liquid does not spread but forms a spherical surface. Thephenomenon of wetting varies considerably depending on properties of thesurface of the solid and properties of the liquid.

As shown in FIG. 6A, a relationship among forces indicated by threearrows are in balance in the case where the liquid on the surface of thesolid forms a spherical surface, and the forces are represented by thefollowing Equation using Young's modulus.γ_(S)=γ_(SL)+γ_(L) cos θ  Equation 1

In Equation 1, γ_(S) is a surface tension of the solid, γ_(SL) is asurface tension of the liquid, γ_(L) is an interfacial tension, and θ isa contact angle.

FIGS. 6B to 6D respectively show convex lenses formed on through holes,convex lenses formed on truncated conical through holes and concavedlenses formed on through holes. Hereinafter, a volume of each of thethrough holes of FIGS. 6B to 6D is indicated by Vb, Vc and Vd; a volumeof the lens material dropped or injected to each of the through holes isindicated by Lb, Lc and Ld; and the contact angles of FIGS. 6B to 6D arerespectively indicated by θ_(B, θ) _(C) and θ_(D).

When Lb is larger than Vb, the convex lenses as shown in FIG. 6B areformed, and the following Equation holds.γ_(S)=γ_(L) cos θ_(B), γ_(S)=γ_(L) sin θ_(B)  [Equation 2]

When Lb is larger than Vb and each of the through holes has thetruncated conical shape as shown in FIG. 6C, it is possible to formconvex lenses each having a curvature different from that of the convexlenses of FIG. 6B, and the following Equation holds.γ_(S)=γ_(L) cos θ_(C)+γ_(SL) cos α, γ_(L) sin θ_(C)=γ_(SL) sinα.  [Equation 3]

When Lb is equal to or smaller than Vb, the concaved lenses are formedas shown in FIG. 6D, and the following Equation holds. In this case, thedirection of γ_(SL) is considered to be transverse.γ_(S)=γ_(L) cos θ_(D), γ_(SL)=γ_(L) sin θ_(D)  [Equation 4]

Thus, it is possible to form both of the convex lenses and the concavedlenses by properly adjusting the viscosity, the wettability to thesubstrate material and the dropping amount of the lens material. Furtherit is possible to produce lenses each having a large numerical aperture(NA) since the curvature of lenses can be changed as described above.

A basic conception of adhesiveness according to the present inventionwill be described below. When water or alcohol is dropped on a surfaceof a solid that has a relatively large surface energy such as a cleanglass or metal, the liquid wets completely the surface of the solid.When a solid-gas interfacial energy is γ_(SG), a gas-liquid interfacialenergy is γ_(LG) and a solid liquid interfacial energy is γ_(SL), thefollowing Equation holds and the surface of the solid is not wet torepel the liquid.γ_(SG)<γ_(LG)+γ_(SL)  [Equation 5]When a liquid spreads over a surface of a solid, the phenomenon iscalled “spread wetting”. To contrast, in the case where a liquidimmerses into capillaries of a fiber or a paper, the phenomenon iscalled “immersional wetting”. In turn, in the case of the presentinvention, a liquid adheres on a surface of a solid in the form ofspheres, and the phenomenon is called “adhesive wetting”.

The spread wetting occurs when water is dropped on a clean glasssurface; however, it is possible to cause the adhesive wetting on theglass surface by subjecting the surface to a hydrophobication by using acationic-activating agent. A change in a free energy ΔG with respect toeach of the wettings is obtained by subtracting an interfacial energythat is lost by each of the wettings from an interfacial energy causedby each of the wettings. Particularly, the change in a free energy ΔGwith respect to the adhesive wetting is represented by the followingEquation.ΔG=γ _(SL)−γ_(SG)γ_(LG)  [Equation 6]Here, since Equation 1 can be rewritten into γ_(SG)=γ_(SL)+γ_(LG) cos θby using γ_(SG) and γ_(LG), Equation 6 can be modified as follows.ΔG=−γ _(LG)(1+cos θ)  [Equation 7]

It is apparent from Equation 7 that the change in free energy withrespect to the adhesive wetting can be represented as a coefficient forthe surface tension of the liquid and a contact angle θ and it ispossible to cause the adhesive wetting when ΔG is a positive integer.Accordingly, the adhesive wetting can occur irrespective of θ. However,a reduction in the free energy is relatively large and the wetting tendsto occur if a value of θ is relatively small.

(Fifth Embodiment)

In order to control the lens curvature, it is possible to use throughholes 62 each having a step-like profile in place of the tapered throughholes. Examples of forming convex lenses 65 are described hereinbefore;however, it is possible to form not only the convex lenses but alsoconcaved lenses and non-spherical lenses by adjusting the amount drop orinjection of the lens material.

In the above embodiments, cases of using the adhesive resin material asthe lens material for the microlenses composing the microlens array aredescribed; however, it is also possible to use a plastic material, aglass material or the like as the lens material by changing thesubstrate material, the cure time and the dropping amount.

Cases of using the plastic material, glass material and so forth will bedescribed below with reference to FIG. 3A to 3E. In the case of using aplastic as the material for the convex lenses, it is necessary to add tothe nozzles 33 a function of heating the lens material to or over apredetermined temperature so that the plastic is liquefied. Also, inorder to form the lenses without fail, it is necessary to heat thesubstrate 31 in advance so that the plastic material dropped or injectedthereto is not solidified too rapidly by cooling. Further, in the caseof using a glass material as the lens material, it is necessary to heatthe glass material to or over a predetermined temperature beforedropping or injecting the glass material from the nozzles 33. Also, inorder to form the lenses without fail, it is necessary to heat thesubstrate 31 in advance so that the glass material dropped or injectedthereto is not solidified too rapidly by cooling.

Also, it is possible to use a silicone substrate, a ceramic material, aplastic material, a fiber reinforced plastic, a fiber material such as acarbon fiber or a composite material composed of the above materials asthe substrate material in place of the glass material. Examples of thefiber composite material include a glass fiber reinforced plastic (GFRP)that has widely been used. A composite material obtainable by combininghigh-performance and high-functional materials is called “advancedcomposite material” (ACM), and it is possible to use as the substratematerial an ACM comprising a reinforcing material such as ahigh-performance carbon fiber, an aramid fiber and like inorganic fibersand a whisker as well as a matrix such as various high-performanceresins, metals and ceramics.

(Sixth Embodiment 6)

It is possible to produce a microlens array employing the productionmethod described with reference to FIGS. 3A to 3E using a substrate 71on which hexagon-shaped through holes 72 are formed as shown in FIG. 8,the substrate being formed from a flexible fiber material. Particularlyin this case, it is possible to produce a flexible microlens sheet as alens material to fill the through holes 72 to form lenses 73 by using aflexible resin material or a flexible plastic material havinglight-transmitting properties. Further, it is possible to manufacture acompound eye (similar to that of an insect which has a curved surface)image recognition device by so forming subminiature CCD elements thatthe CCD elements respectively correspond to the microlenses formed onthe flexible microlens sheet.

A case of laminating two microlens arrays will be described below withreference to FIGS. 9A and 9B. FIG. 9A shows a state wherein twomicrolens arrays, on which the convex lenses are formed as describedabove, are laminated in such a manner that their back faces contact toeach other and their optical axes coincide with each other. Bylaminating the two microlens arrays in the above-described manner, it ispossible to enhance an optical coupling efficiency when used for theoptical coupling. In order to further enhance the coupling efficiency,it is possible to use a spacer 89 to laminate the two microlens arrays.In this case, a distance between lenses can be adjusted by using thespacer 89 to further enhance the coupling efficiency. Also, by the useof the spacer 89, it is possible to produce a microlens array sheet bycombining double-convex lenses varying in shape.

(Eighth Embodiment)

FIGS. 10A to 10D show production patterns of microlens array accordingto an eighth embodiment of the present invention. FIG. 10A shows apattern wherein microlenses 92 that are identical in size are formed ona substrate 91 at a same pitch and a constant interval. The patterns areapplicable to 1×N array lenses and N×N array lenses for the use as anoptical interconnection for a parallel optical fiber transmissionbetween chips, modules, boards and the like. Therefore, although themicrolenses are typically formed at a pitch of 125 microns or 250microns, it is possible to form the through holes at an arbitrary pitch.

Further, as shown in FIG. 10B, it is possible to form a combined arraypattern of small diameter microlenses 93 and large diameter microlenses94 for the use as an incident beam array whose light source or incidentlight has a sporadic beamform. The microlenses of arbitrary sizes thatvary in diameter can be used in combination by adjusting processingsizes of the through holes to be formed on the substrate 91.

As shown in FIG. 10C, it is also possible to produce a lens array byshortening an interval between a microlens 94 and an adjacent microlens95. Further, as shown in FIG. 10D, it is possible to dispose microlensesin the manner of fine fill disposition as shown in FIG. 8 by movingmicrolenses 96 of a first array and microlenses 97 of a second array. Itis possible to further improve characteristics of the microlens array byforming a lens array by the use of a several types of lenses incombination in accordance with the properties of the light source andincident beam, the several types of lenses being those formed of lensmaterials that vary in optical properties i.e. refractive index andwavelength transmitting properties or those of different sizes.

(Ninth Embodiment)

A manufacturing method of microlens array according to a ninthembodiment of the present invention will be described with reference toFIGS. 11A to 11C. The process illustrated in FIGS. 11A to 11C isdifferent from that illustrated in FIGS. 4A to 4C in lenses to beformed, i.e., composite lenses that vary in refractive index are formedin the process of FIGS. 11A to 11C. A plurality of spherical microlensarrays 111 is formed two-dimensionally as shown in FIG. 11A, and thenthe microlens array substrate is reversed as shown in FIG. 11B. Afterthat, the composite lenses are formed by dropping the materials 113 thatvary in refractive index as shown in FIG. 1C. Thus, it is possible toform the microlens array of composite refractive index by using thematerials that vary in refractive index in combination. Accordingly, thelenses formed from the materials varying in refractive index function asachromatic lenses, thereby realizing microlenses capable of reducingchromatic aberration.

(Tenth Embodiment)

A manufacturing method of microlens array according to a tenthembodiment of the present invention will be described with reference toFIGS. 12A and 12B. The process illustrated in FIGS. 12A and 12B isdifferent from that illustrated in FIGS. 5A to 5D in through holes,i.e., as shown in FIG. 12A, each of through holes 122 has a rectangularshape and long sides of each of the through holes 122 have tapering 123.Since the through holes have the rectangular shape and long sidesthereof are tapered as described above, convex lenses formed on thethrough holes by dropping a lens material each having an oval curvatureas lenses 124 shown in FIG. 12B. The oval lenses 124 thus formedfunction as anamorphotic lenses and capable of shaping a beam that isemitted from a semiconductor laser and asymmetric in lengthwise andcrosswise to be symmetric, thereby enhancing coupling efficiency with anoptical fiber or a light reception element to a remarkably high degree.In addition, although the anamorphotic lenses are shown in FIG. 12B, itis possible to form cylindrical lenses by modifying the shapes ofthrough holes.

(Eleventh Embodiment)

A manufacturing method of microlens array according to an eleventhembodiment of the present invention will be described with reference toFIGS. 13A and 13B. The method illustrated in FIGS. 13A and 13B isdifferent from that illustrated in FIGS. 5A to 5D in a substratestructure, i.e., the substrate structure shown in FIGS. 13A and 13 b isa three layer structure formed by subjecting a surface of a solidsubstrate 134 that is relatively low in solid-liquid interfacial energyto an inactivating treatment to cause the adhesive wetting. By the threelayer structure achieved by the inactivating treatment of the surface133, a portion of the surface 133 at which through holes are not formedrepels a lens material 135 to thereby contribute to fixing the lensmaterial 135 in the through holes. Examples of the inactivatingtreatment include a method of increasing roughness by irradiating asolid surface with an electron beam and a method of coating a solidsurface for inactivation. Other effective treatment may be sputtering,plasma CVD method, eximer laser irradiation, formation of a coating thatis highly hydrophobic, formation of an oxide membrane with respect tometals, anodizing method with respect to metals, formation offluoridated amorphous carbon membrane by the plasma CVD method, platingand the like. Thus, as a result of the surface treatment of thesubstrate surface as described above, the formation of the lenses isfacilitated by the inactivation of the substrate with respect to thelens material to make it possible to form uniform lenses. In the casewhere the solid surface is a smooth surface and a contact angle of thelens material is 90 degrees or more, the smooth surface may be subjectedto a roughing treatment to increase the contact angle. Accordingly, itis also possible to increase the adhesive wetting properties by formingfine convexoconcaves of a several microns or less on the smooth surfaceby a metal pattern processing, etc., thereby simplifying a formation ofspherical lenses 135 on the through holes.

The substrate to be used for the above embodiments is not limited to theglass substrate, and a monocrystal silicone substrate, a ceramicsubstrate, a plastic substrate, a fiber substrate, a metal substrate ora composite substrate can be used depending on the lens material to beused. It is apparent that the microlens array is obtainable by using anyone of the above substrates provided that the method for forming thethrough holes and the lens material are properly selected.

As described above, it is possible to arbitrarily change the size of themicrolens of the present invention depending on the size of each ofthrough holes to be formed on the substrate, and it is possible toproduce the microlenses of a wide range of sizes each of which has adiameter from a several tens of microns to a several millimeters. It ispossible to control optical properties of the microlens array by way ofthe lens material to be dropped or injected to the substrate, and eachof the microlenses thus obtained is remarkably advantageous in terms ofthe optical coupling since both surfaces of each of the lenses are opento air without contacting the substrate material. Accordingly, the usageof the microlens array of the present invention is not limited to theoptical communication elements, and it is possible to apply themicrolens array to the optical packaging substrates and also, widely toimage information processing devices and liquid crystal display devices,for the optical coupling, optical signal processing, light beamconversion and the like.

As is apparent from the above description, the present inventionprovides the microlens array that realizes downsized andhigh-performance optical coupling elements to be used in the fields ofthe optical communication, the optical packaging and the like and themethod of manufacturing the same.

That is, according to the present invention, it is possible to produce amicrolens array of a wide range of lens diameters remarkably easily.Also, according to the present invention, the lenses are disposed atarbitrary positions with both surfaces of each of the lenses being opento air without contacting the substrate material and they are remarkablyhigh in precision. Thus, the present invention realizes the downsizedand high-performance optical coupling elements.

1. A microlens multilayer formed by laminating a plurality of microlensarrays produced by a method of manufacturing a microlens array accordingto the following steps: (a) dropping or injecting a liquefied lensmaterial into a plurality of through holes formed on a substrate so asto dispose the lens material at each of the through holes, the lensmaterial having a predetermined transmittivity and a predeterminedviscosity, and (b) laminating the plurality of microlens arrays so thatoptical axes of the microlenses of each microlens array coincide withthe optical axes of corresponding microlenses of another microlensarray.
 2. A microlens array comprising a substrate in which a pluralityof through holes are formed and a plurality of microlenses respectivelydisposed at the through holes in the substrate, wherein the microlensesare fixed to the through holes of the substrate by way of adhesion ordeposition of a microlens material to a substrate material.
 3. Themicrolens array according to claim 2, wherein the microlenses are formedof a ultraviolet ray curable resin material, a thermosetting resinmaterial, a thermoplastic material or a glass material.
 4. The method ofmanufacturing a microlens array according to claim 2, wherein each ofthe through holes has a truncated conical shape or a step portion. 5.The method of manufacturing a microlens array according to claim 2,wherein the microlenses are convex lenses.
 6. The method ofmanufacturing a microlens array according to claim 2, wherein themicrolenses are concave lenses.
 7. The method of manufacturing amicrolens array according to claim 2, wherein all refractive indexesand/or a transmittivities of the lens materials to be dropped orinjected to the plurality of through holes are not same.
 8. The methodof manufacturing a microlens array according to claim 2, wherein a wholeor a part of the plurality of through holes vary in size and a whole ora part of the microlenses vary in size in accordance with the sizes ofthe through holes.
 9. The method of manufacturing a microlens arrayaccording to claim 2, wherein the plurality of through holes arearranged in the substrate to give a closest packed structure, each ofthe through holes having the shape of a hexagon of a predetermined size.10. The method of manufacturing a microlens array according to claim 2,wherein the substrate is formed of any one of silicone, a thermoplasticmaterial, a glass material, a ceramic material, a fiber material and acomposite material.